A future without human leukocyte antigens?^☆

Platelet transfusion is an essential supportive therapy for patients with hemato-oncological disorders as many of them present with thrombocytopenia and bleeding. Platelet refractoriness, defined as the lack of adequate post-transfusion platelet count increment, remains a challenge in the management of platelet transfusion dependent patients. The majority of refractory cases have nonimmune causes and include infection/sepsis, fever, splenomegaly, use of antibiotics and even storage conditions.¹ Immune causes comprise ABO incompatibility, antibodies against class I human leukocyte antigens (HLA) (mostly HLA-A and HLAB), and antibodies against human platelet antigens (HPA). In hematology/oncology patients, platelet refractoriness has been reported in 7-34% of cases.²

The transfusion needs of patients with immune platelet refractoriness triggers a series of processes that include the identification of the immune cause, the search for and notification of compatible donors in a genotyped donor bank, the donation of the actual blood product and finally its release and availability for use. These are lengthy procedures, which are costly and often unsuccessful. On the other hand, we have the refractory patient, bleeding or at imminent risk of bleeding, where urgency and agility are essential. These are two dissonant situations attempting to converge on the same goal. In this regard, despite the few studies that rigorously assess bleeding in patients requiring cross-matched platelet support, the refractory state is associated with increased mortality.³

Thus, the development of technologies that aim to optimize the availability of the blood product as described by Ferreira et al. who report the use of a tool which identifies potential donors even with a limited database of genotyped donors, are extremely welcome in transfusion medicine and are important weapons in the management of these cases.⁴ Nevertheless, processing constraints remain and are the basis for potentially fatal situations.

Against this background, solutions must be obtained. The ex vivo production of HLA-free transfusion products represents an alternative.

In 1995, Choi et al. described the possibility of generating CD34⁺ hematopoietic progenitor cell (HPC)-derived platelets in vitro using thrombopoietin (TPO) and a specific cytokine cocktail.⁵ Since then, many groups have investigated the feasibility of producing platelets from umbilical cord blood, peripheral blood progenitor cells, bone marrow progenitor cells and human embryonic stem cells.^6-10

Recently, the feasibility of generating mature functional megakaryocytes from human pluripotent stem cells has been demonstrated.^11,12 Human induced pluripotent stem cells (iPSCs) represent an unlimited cell source for the production of blood products. Additionally, iPSC-based blood pharming approaches have been combined with genome editing technology.¹³ Despite the fact that all of these approaches hold a great potential in the field of transfusion, the probable HLA-incompatibility with the recipient remains a major hurdle to their future application. To circumvent this problem there is an interesting proposal to generate platelets by using transcription activator-like effector nuclease (TALEN)-mediated targeted disruption of the β2 microglobulin gene. Knocking out β2M expression eliminates HLA class I cell-surface expression, which is thought to be a major cause of platelet refractoriness.² Figueiredo et al. demonstrated a stable reduction of HLA class I surface expression obtained by using a combination of lentiviral gene transfer and RNA interference technology to target the conserved β2m molecule which is an essential part of dimeric HLA class I molecules.⁹ By this methodology, the authors revealed the capacity of HLA-silenced megakaryocytes, such as platelets, to escape anti-HLA antibody-mediated cytotoxicity.

Altogether, these studies show the feasibility of pharming producing engineered platelets in vitro with advantageous features that promote their maximal therapeutic efficacy. The next challenge in this field is the production of clinically relevant platelet numbers. Indeed, some research groups have already shown the feasibility of producing platelets in bioreactors.^14,15 Their use for the large-scale production of universal platelets may open a new horizon in the field of transfusion medicine.

• ☆
  See paper by Ferreira MG et al. on pages 298-304.

References

• ¹
  Slichter SJ, Davis K, Enright H, Braine H, Gernsheimer T, Kao KJ, et al. Factors affecting posttransfusion platelet increments, platelet refractoriness, and platelet transfusion intervals in thrombocytopenic patients. Blood. 2005;105(10):4106-14.
• ²
  Hod E, Schwartz J. Platelet transfusion refractoriness. Br J Haematol. 2008;142(3):348-60.
• ³
  Kerkhoffs JL, Eikenboom JC, Van De Watering LM, Van Wordragen-Vlaswinkel RJ, Wijermans PW, Brand A. The clinical impact of platelet refractoriness: correlation with bleeding and survival. Transfusion. 2008;48(9):1959-65.
• ⁴
  Ferreira MG, De Vito FB, Ferreira AA, Bub CB, Dos Santos FA, Botelho Filho A, et al. Applicability of an instrument to identify human leukocyte antigen-compatible donors for platelet transfusions. Hematol Transfuns Cell Ther. 2018;40:298-304.
• ⁵
  Choi ES, Nichol JL, Hokom MM, Hornkohl AC, Hunt P. Platelets generated in vitro from proplatelet-displaying human megakaryocytes are functional. Blood. 1995;85(2):402-13.
• ⁶
  Matsunaga T, Tanaka I, Kobune M, Kawano Y, Tanaka M, Kuribayashi K, et al. Ex vivo large-scale generation of human platelets from cord blood CD34 ⁺ cells. Stem Cells. 2006;24(12):2877-87.
• ⁷
  De Bruyn C, Delforge A, Martiat P, Bron D. Ex vivo expansion of megakaryocyte progenitor cells: cord blood versus mobilized peripheral blood. Stem Cells Dev. 2005;14(4):415-24.
• ⁸
  Norol F, Vitrat N, Cramer E, Guichard J, Burstein SA, Vainchenker W, et al. Effects of cytokines on platelet production from blood and marrow CD34+ cells. Blood. 1998;91(3):830-43.
• ⁹
  Figueiredo C, Goudeva L, Horn PA, Eiz-Vesper B, Blasczyk R, Seltsam A. Generation of HLA-deficient platelets from hematopoietic progenitor cells. Transfusion. 2010;50(8):1690-701.
• ¹⁰
  Lu SJ, Li F, Yin H, Feng Q, Kimbrel EA, Hahm E, et al. Platelets generated from human embryonic stem cells are functional in vitro and in the microcirculation of living mice. Cell Res. 2011;21(3):530-45.
• ¹¹
  Moreau T, Evans AL, Vasquez L, Tijssen MR, Yan Y, Trotter MW, et al. Large-scale production of megakaryocytes from human pluripotent stem cells by chemically defined forward programming. Nat Commun. 2016;7:1-15.
• ¹²
  Baigger A, Blasczyk R, Figueiredo C. Towards the manufacture of megakaryocytes and platelets for clinical application. Transfus Med Hemother. 2017;44(3):165-73.
• ¹³
  Feng Q, Shabrani N, Thon JN, Huo H, Thiel A, Machlus KR, et al. Scalable generation of universal platelets from human induced pluripotent stem cells. Stem Cell Rep. 2014;3(5):817-31.
• ¹⁴
  Thon JN, Mazutis L, Wu S, Sylman JL, Ehrlicher A, Machlus KR, et al. Platelet bioreactor-on-a-chip. Blood. 2018;124(12):1857-68.
• ¹⁵
  Nakagawa Y, Nakamura S, Nakajima M, Endo H, Dohda T, Takayama N, et al. Two differential flows in a bioreactor promoted platelet generation from human pluripotent stem cell-derived megakaryocytes. Exp Hematol. 2013;41(8):742-8.

Publication Dates

• Publication in this collection
  Oct-Dec 2018